SWEETSPOT: NEAR-INFRARED OBSERVATIONS OF 13 TYPE Ia SUPERNOVAE FROM A NEW NOAO SURVEY PROBING THE NEARBY SMOOTH HUBBLE FLOW

The discovery of the accelerating expansion of the universe with Type Ia supernovae (SNe Ia; Riess et al. 1998; Perlmutter et al. 1999) has sparked a decade and a half of intensive Type Ia supernova (SN Ia) studies to pursue the nature of dark energy. High-redshift SN Ia surveys attempt to measure the equation-of-state parameter to sufficiently distinguish among dark energy models. The majority of this work has been focused on standardizing the rest-frame optical luminosities of SNe Ia. The goal of low-redshift surveys has been to both provide the distance anchor for high-redshift relative distance measurements, and to better-calibrate SNe Ia as standard candles through an improved understanding of SNe Ia themselves.

As the amount of available SN Ia data has grown dramatically, systematic uncertainties have come to dominate cosmological distance measurements with SNe Ia (Albrecht et al. 2006; Astier et al. 2006; Wood-Vasey et al. 2007; Kessler et al. 2009; Sullivan et al. 2010; Conley et al. 2011). A well-established systematic affecting SNe Ia is dust reddening and extinction (see, for example, Jha et al. 2007; Conley et al. 2007; Wang et al. 2006, 2009; Goobar 2008; Hicken et al. 2009; Folatelli et al. 2010; Foley & Kasen 2011; Chotard et al. 2011; Scolnic et al. 2014). It is difficult to separate the effects of reddening as a result of dust from intrinsic variation in the colors of SNe Ia. Unfortunately, most observations of SNe Ia are made in the rest-frame optical and UV where reddening corrections are large.

SNe Ia are superior distance indicators in the near-infrared (NIR),⁵ with more standard peak JHK_s magnitudes and relative insensitivity to reddening (Meikle 2000; Krisciunas et al. 2004a, 2007) than in the rest-frame optical passbands traditionally used in SN Ia distance measurements. Additionally, Krisciunas et al. (2004a) found that objects that are peculiar at optical wavelengths such as SN 1999aa, SN 1999ac, and SN 1999aw appear normal at infrared wavelengths. Although it appears that the 2006bt-like subclass of SNe have normal decline rates and V-band peak magnitudes, they display intrinsically red colors and have broad, slow-declining light curves in the NIR similar to super-Chandra SNe Ia (Foley et al. 2010; Phillips 2012).

These early results have motivated several efforts to pursue large samples of SNe Ia observed in the rest-frame NIR with 1.3–2.5 m telescopes: the Carnegie Supernova Project (CSP-I, II; Contreras et al. 2010; Folatelli et al. 2010; Stritzinger et al. 2011; Kattner et al. 2012); Center for Astrophysics (CfA; Wood-Vasey et al. 2008); Peters Automated Infrared Imaging Telescope (RAISIN; Kirshner et al. 2012). The results from these projects to date indicate that SNe Ia appear to be standard NIR candles to ≲ 0.15 mag (Wood-Vasey et al. 2008; Folatelli et al. 2010; Kattner et al. 2012), particularly in the H band. NIR observations of SNe Ia are a current, significant focus of nearby studies of SNe Ia. Recent work by Barone-Nugent et al. (2012) used 8 m class telescopes to observe 12 SNe Ia in the NIR from 0.03 < z < 0.08 and found promising evidence that the H-band peak magnitude of SNe Ia may have a scatter as small σ_H = 0.085 mag. This work demonstrated the benefit of using larger-aperture telescopes in overcoming the significantly increased background of the night sky in the NIR.

In this paper, we introduce a new effort to observe SNe Ia in the NIR in the nearby smooth Hubble flow. "SweetSpot" is a 72 night, 3 yr National Optical Astronomy Observatory (NOAO) Survey program (2012B-0500) to observe SNe Ia in JHK_s using the WIYN 3.5 m telescope and the WIYN High-resolution Infrared Camera (WHIRC). Our goal is to extend the rest-frame H-band NIR Hubble diagram to z ∼ 0.08 to (1) verify recent evidence that SN Ia are excellent standard candles in the NIR, particularly in the H band; (2) test if the recent correlation between optical luminosity and host galaxy mass holds in the NIR; (3) improve our understanding of intrinsic colors of SNe Ia; (4) study the nature of dust in galaxies beyond our Milky Way; (5) provide a standard, well-calibrated NIR rest-frame reference for future, higher-redshift supernova surveys.

In this paper, we present results from our 2011B pilot proposal. In Section 2, we discuss our data reduction and present light curves of 13 SNe Ia. To this sample we add data from the literature (Section 3) and fit the light curves using SNooPy (Burns et al. 2011). Details of how we perform the fitting are discussed in Section 4. We present our results, including an H-band Hubble diagram, in Section 5. We discuss our overall SweetSpot program strategy and goals along with future prospects for rest-frame H-band SN Ia observations in Section 7, and conclude in Section 8.

2.1. Observations and Sample Selection

2.2. Image Processing and Coaddition

The data were reduced in IRAF⁸ following the steps outlined in the WHIRC Reduction Manual (Joyce 2009).

• 1.  
  The raw images were trimmed of detector reference pixels outside the main imaging area and corrected for the sub-linear response of the array.
• 2.  
  The ON dome flats were combined; the OFF dome flats were combined; and the OFF combined dome flat was then subtracted from the ON combined dome flat to yield the pixel-by-pixel response.
• 3.  
  The pupil ghost (an additive artifact resulting from internal reflection within the optical elements of WHIRC) was removed from this response using the IRAF routine mscred.rmpupil.
• 4.  
  For each target, the set of dithered science images were used to generate a median-filtered sky frame. The individual science images were then sky-subtracted and flat-fielded using these median frames.
• 5.  
  The geometric distortion resulting from a difference in plate scales in the x and y coordinates and field distortion at the input to WHIRC was corrected using the IRAF routine geotran and the pre-computed WHIRC geometric distortion calibration from 2009 March 5.⁹
• 6.  
  The individual science images were stacked using the IRAF routine upsqiid.xyget to find the common stars in the images and create a registration database between the individual images in an observation sequence. Intensity offsets were determined from the overlap regions in the registration database and the set of individual images were combined into a composite image using the IRAF routine upsqiid.nircombine. An exposure map of a typical stacked observation sequence can be found in Figure 1.

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Representative postage stamp images from the processed H-band composite images of our supernovae are shown in Figure 2.

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2.3. Photometry and Calibration

We measured the detected counts of the SNe Ia and the stars in the field with aperture photometry on the stacked images using the Goddard Space Flight Center IDL Astronomy User's Library routines gcntrd and aper.¹⁰ We used an aperture diameter of 1.5 FWHM (FWHM values were typically around 2'') and measured the background in a surrounding sky annulus from 1.5 FWHM + 01 to 1.5 FWHM + 06. These counts in ADU/(60 s) equivalent exposure were converted to instrumental magnitudes m_{inst, f} = −2.5log₁₀ADU/60 s.

To calibrate the instrumental magnitudes, we first define a transformation between the WHIRC and the Two Micron All Sky Survey (2MASS; Skrutskie et al. 2006) systems using the following equation:

$$\begin{eqnarray} && m^{\rm 2MASS}_f - m_{{\rm inst,}f}^{\rm WHIRC} = {\rm zpt}_f + k_f (X-1) \nonumber \\ && \quad + c_f \left(\left(m_J^{\rm 2MASS} - m_H^{\rm 2MASS}\right) - 0.5\,{\rm mag}\right), \end{eqnarray} \tag{ 1 }$$

where f designates the filter, X is the airmass, and the 2MASS color is compared to a reference of $m_J^{\rm 2MASS}\, {-}\, m_H^{\rm 2MASS}=0.5$ mag, which represents the typical color of stars in our fields as well as SNe Ia after maximum. We then jointly solve for the zero point (zpt), airmass coefficient (k),¹¹ and color coefficient (c) using all instrumental magnitudes measured from 2MASS stars in the fields from our 2011 November 15 and 2012 January 8 nights. This procedure was performed separately for each filter following Equation (1).

Our fit for each filter is plotted in Figure 3 and our fit results are summarized in Table 4. We find non-zero color terms of c_J = 0.062 ± 0.035 and c_H = −0.186 ± 0.043 between the 2MASS and WHIRC systems, and airmass coefficients of k_J = −0.051 ± 0.020 mag airmass⁻¹ and k_H = −0.066 ± 0.030 mag airmass⁻¹.

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Matheson et al. (2012) used the same WIYN+WHIRC system to observe the very nearby SN 2011fe in M101, and used "canonical" values of $(k_J, k_H, k_{{K_s}})=(-0.08,-0.04,-0.07)$ mag airmass⁻¹ (in our sign convention for k). These values were based on a long-term study of k_J, k_H, and k_K at KPNO in the 1980s using single-channel NIR detectors. This effort found a range of values of −0.12 < k_J < −0.07 mag airmass⁻¹, −0.08 < k_H < −0.04 mag airmass⁻¹, and −0.11 < k_K < −0.07 mag airmass⁻¹ with a significant seasonal variation dependent on the precipitable water vapor (R. R. Joyce and R. Probst 2013, private communication). The filters used in these measurements were wider than the standard 2MASS filters or WHIRC filters we use here. The narrow WHIRC filters do not include some of the significant water-vapor absorption regions included in the NIR filters used in the 1980s KPNO study, and thus would reasonably be expected to have a smaller absolute value of k_J. Our determined k_J and k_H values are thus consistent with these previous results. However, the variation of k in the NIR as a result of water vapor strongly motivates future improvements in tracking precipitable water vapor and NIR extinction to improve the instantaneous determination of k.

We then selected a star in each field that was near the supernova and had a similar color to the supernova at the time of our observations. These reference stars are listed in Table 5. We used the best observation of the reference star, our fit results from Table 4, and Equation (1) to create a list of calibrated standard stars in the WHIRC natural system. We note that our only observation of SN 2011io was taken under partial clouds. For a given field, the standard star was then used to find the zero point for each stacked image as follows:

$$\begin{equation} {\rm zpt}_{f,i} = m_{{\rm cal},f}^{\rm WHIRC} - m_{{\rm inst},f,i}^{\rm WHIRC}, \end{equation} \tag{ 2 }$$

where the i subscript indicates stacked image and m_cal is the calibrated standard star for that field. This zero point was then applied to the measured instrument magnitude from the supernovae to generate the calibrated supernova magnitude in the WHIRC natural system. These light curves are presented in Table 6.

We report magnitudes in the WIYN+WHIRC natural system.¹²

To our sample of WHIRC SNe Ia we add the following data from the literature.

• 1.  
  A compilation of 23 SNe Ia from Jha et al. (1999), Hernandez et al. (2000), Krisciunas et al. (2000, 2004a, 2004b), Phillips et al. (2006), Pastorello et al. (2007a, 2007b), and Stanishev et al. (2007). This is the same set that was used as the "literature" sample by Wood-Vasey et al. (2008). We use 22 SNe Ia from this set, one of which was observed by the (CSP. We refer to the 21 SNe Ia that are unique to this sample as K+ in recognition of the substantial contributions by Kevin Krisciunas to this sample and the field of NIR SNe Ia.
• 2.  
  Wood-Vasey et al. (2008) presented JHK_s measurements of 21 SNe Ia from the CfA Supernova Program using the robotic 1.3 m PAIRITEL (Bloom et al. 2006) at Mount Hopkins, Arizona. We use 17 SNe Ia from this sample which we refer to as WV08.
• 3.  
  Contreras et al. (2010) and Stritzinger et al. (2011) present 69 SNe Ia from the CSP using observations at the Las Campanas Observatory in Chile (Hamuy et al. 2006). The CSP observations in YJHK_s were carried out with the Wide Field Infrared Camera attached to the du Pont 2.5 m Telescope and RetroCam on the Swope 1 m telescope supplemented by occasional imaging with the PANIC NIR imager (Osip et al. 2004) on the Magellan Baade 6.5 m telescope. We use 55 SNe Ia from this sample, 6 of which are also in WV08. We refer to the 49 SNe Ia that were not observed by Wood-Vasey et al. (2008) as CSP.
• 4.  
  Barone-Nugent et al. (2012) extended the rest-frame NIR sample out to z ∼ 0.08 with 12 SNe Ia observed in JH on Gemini Observatory's 8.2 m Gemini North with the NIR Imager and Spectrometer (Hodapp et al. 2000) and on ESO's 8.1 m Very Large Telescope using HAWK-I (Casali et al. 2006). We use these 12 SNe Ia and refer to this set as BN12.

To arrive at these samples, we removed supernovae that were reported to have a spectrum similar to the sub-luminous SN 1991bg (SN 2006bd, SN 2007N, SN 2007ax, SN 2007ba, SN 2009F); were reported to have a spectrum that was peculiar (SN 2006bt, SN 2006ot); were identified as possible super-Chandrasekhar mass objects (SN 2007if, SN 2009dc); were determined to be highly reddened (SN 1999cl, SN 2003cg, SN 2005A, SN 2006X); or were found to have a decline rate parameter Δm₁₅ > 1.7 (SN 2005bl, SN 2005ke, SN 2005ku, SN 2006mr) according to the information provided in Folatelli et al. (2010), Contreras et al. (2010), Stritzinger et al. (2011), and Burns et al. (2011). We also removed SN 2002cv that Elias-Rosa et al. (2008) found to be heavily obscured and SN 2007hx whose photometry is unreliable (M. Stritzinger 2013, private communication). A redshift histogram of this entire sample, which represents the currently available collection of published normal NIR SNe Ia, is plotted in Figure 4. Note that with WIYN+WHIRC we can reach out to z ∼ 0.09 and cover the entirety of the nearby smooth Hubble flow from 0.03 < z < 0.08.

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We used the quoted system transmission function reported by each survey. For SNe Ia that were observed by multiple surveys, we fit all of the available photometry for the SN Ia.

We fit the light curves using the suite of supernova analysis tools developed by CSP called SNooPy (Burns et al. 2011). We fit the data using SNooPy (version 2.0–267) "max_model" fitting that uses the following model m_X:

$$\begin{eqnarray} && m_X(t-t_{\rm max}) = T_Y((t^{\prime }-t_{\rm max})/(1+z),\Delta m_{15}) + m_Y \nonumber \\ &&\quad + R_XE(B-V)_{\rm Gal} + K_{X,Y}(z,(t^{\prime }-t_{\rm max})/(1+z),\nonumber \\ &&\quad E(B-V)_{\rm host}, E(B-V)_{\rm Gal}), \end{eqnarray} \tag{ 3 }$$

where t is time in days in the observer frame, T_Y is the SNooPy light-curve template, m_Y is the peak magnitude in filter Y, t_max is the time of maximum in the B band, Δm₁₅ is the decline rate parameter (Phillips 1993), E(B − V)_Gal and E(B − V)_host are the reddening resulting from the Galactic foreground and the host galaxy, R_X is the total-to-selective absorption for filters X, and K_{X, Y} is the cross-band K-correction from rest-frame X to observed Y. The free parameters in this model are t_max, Δm₁₅, and m_Y. We do not assume any relationship between the different filters and therefore do not apply any color correction. We generate the template T(t, Δm₁₅) from the code of Burns et al. (2011) which generates rest-frame templates for J and H from the CSP data (Folatelli et al. 2010).

We use SNooPy to perform the K-corrections on all of the data using the Hsiao et al. (2007) spectral templates. We do not warp or "mangle" the spectral template to match the observed color when performing the K-corrections. A simpler approach makes sense as we are interested in measuring the peak brightness using one NIR band and a prior on t_max. In Figure 5 we plot the H-band filter transmission for the different surveys in our sample. Overlaid are synthetic spectra at various redshifts. Note the difference in widths and up to 0.05 μm shift in the positions of the blue and red edges of the different H-band filters. While SNe Ia are standard in their rest-frame H-band brightness, there is a significant feature at 1.8 μm which moves longward of the red edge of the H-band filter quickly from just z = 0 to z = 0.05. This feature means that it is quite important to have well-understood transmission functions and spectral templates. However, given that the main effect is the feature moving across the edge of the filter cutoff, knowing the filter bandpass provides most of the necessary information without an immediate need for a full system transmission function.

For the 2011B data presented in this paper t_max is fixed to an estimate measured from the spectrum as reported in the ATels/CBETs. This significant prior is necessary as our NIR data only have a few points per light curve (see Table 2), which are not enough to independently estimate t_max. We also fix the light-curve width parameter to Δm₁₅ = 1.1. This is reasonable as we have already eliminated SNe Ia spectroscopically identified as 91bg-like from observations in our own program and from considerations when including the current literature sample. As a result of these priors, only the peak magnitude in each filter (JH) is determined from fitting the light curve (see Table 3). The quoted peak magnitude uncertainties are then determined from least-squares fitting. The light-curve fits to each of the new SNe Ia presented here are shown in Figure 6.

In order to use a consistent method to compare the apparent brightness of the SNe Ia across our entire sample, we applied a similar process for the literature sample. We use a prior on the time of maximum for the K+, CSP, and WV08 data from the SNooPy fit to the B-band light curve alone and fixed Δm₁₅ = 1.1. SN 2005ch is an exception as we do not have a B-band light curve. We fixed the time of maximum for this SN to an estimate from the spectrum reported in Dennefeld & Ricquebourg (2005). The optical light curves are not available for the BN12 data and not all SNe Ia in this sample were reported in ATels. We cannot estimate t_max for a fixed value of Δm₁₅ as we have done for the other samples. Therefore, we fixed the time of maximum and stretch to that reported for these SNe Ia in Maguire et al. (2012).

The peak apparent magnitudes for the 2011B SNe Ia in JH are listed in Table 3. A summary of the light curve fit parameters—which includes the peak apparent magnitude—for the CSP, WV08, BN12, and the present W14 samples can be found in Table 7. The W14 data is the same as that in Table 3, but we include it in Table 7 for the convenience of presenting all of the Hubble diagram information in a single table.

5.1. Near-infrared SN Ia Hubble Diagram

5.2. Absolute H-band Magnitude of a SN Ia

6.1. NIR SN Ia as Standard Candles

6.2. Absolute Brightness

Building off the pilot program presented in this paper, we are currently engaged in a 3 yr, 72 night, large-scale NOAO Survey (2012B-0500; PI: W. M. Wood-Vasey) program to image SNe Ia in the NIR using WIYN+WHIRC. Our goal is to observe ∼150 spectroscopically confirmed nearby SNe Ia in the NIR using WHIRC. We will obtain a total sample of ∼150 SN Ia light curves sampled in JH with 3–6 observations per light curve for the bulk of the sample and a subset of 25 SNe Ia observed in JHK_s out to late phases (> + 30 days) with 6–10 observations per supernova. If SNe Ia are standard in the NIR with to σ_H = 0.1 mag with no significant systematic bias, then 150 SNe Ia in the nearby Hubble flow will allow us to make an overall relative distance measurement to z ∼ 0.05%–1%. Alternatively, we will be able to probe systematics at the few percent level, beyond what we are able to do today in the optical, due to the significant confusion from host galaxy dust extinction and greater dispersion in the SN Ia optical luminosities.

We continue to rely on the hard work of several nearby supernovae surveys to discover and spectroscopically confirm the SNe Ia we observe. Specifically, we follow announcements from the IAU/CBETs and ATels of supernovae discovered and/or classified by KAIT/LOSS (Filippenko et al. 2001), CRTS (Drake et al. 2009) surveys, the intermediate Palomar Transient Factory,¹⁵ Robotic Optical transient search experiment,¹⁶ the Backyard Observatory Supernova Search,¹⁷ the Italian Supernova Search Project,¹⁸ the La Silla Quest survey¹⁹ (Baltay et al. 2012), the CfA Supernova Group²⁰ (Hicken et al. 2012), the Public ESO Spectroscopic Survey of Transient Objects,²¹ the Padova-Asiago Supernova Group,²² and the Nearby Supernova Factory II²³ (Aldering et al. 2002).

We would be happy to work on collaborative efforts to analyze the SNe Ia we are observing with those who have optical light curves and spectra or other NIR data, and invite those interested to contact the first two authors (A.W. and M.W.-V.) to pursue such opportunities.

With this sample, we will extend the SNe Ia NIR H-band Hubble Diagram out to z ∼ 0.08. This will increase the currently published sample size in this "sweet spot" redshift range by a factor of five. The Carnegie Supernova Project II²⁴ is currently engaged in a similar effort to obtain optical+NIR imaging and spectroscopy for a similar sample size in this same redshift range.

While we will obtain 6–10 light curve observations for most of the SNe Ia, we will also explore constructing the "minimal" H-band Hubble diagram. NIR observations are expensive to take from the ground as a result of the significant emission and absorption from the atmosphere, and expensive from space due to the cryogenic detectors often desired. If we could determine distances reliably with just a few NIR data points combined with an optical light curve, we would significantly increase the number of SN Ia distances that could be measured for a given investment of NIR telescope time. We will realistically evaluate this "minimal" required contribution of NIR data to SN Ia cosmology by analyzing the optical light curve with only one or two H-band observations near maximum and check this against the luminosity distance determined from the actual full H-band light curve. The optical light curve will give us the phase and we will measure the brightness in the NIR. If this approach is successful, it opens the window to exploring SNe Ia at higher redshift even given the significant cost of rest-frame NIR observations. We will quantify the improvement of adding one to three NIR observations per SN Ia and make recommendations for the most feasible and beneficial strategy for improving SN Ia cosmology.

If modest observations of only a few rest-frame H-band points along the light curves of a SNe Ia are sufficient enough to provide a robust and relatively precise distance measurement, then there is significant potential in supplementing future, large, ground-based surveys, such as the Large Synoptic Survey Telescope (LSST Science Collaborations et al. 2009), with space-based resources such as the James Webb Space Telescope²⁵ to obtain rest-frame H-band observations to check systematic effects in these large surveys and to independently obtain reliable NIR distances to z > 0.5.

A newly identified systematic affecting inferred optical luminosity distances from SNe Ia is the stellar mass of the host galaxy (Kelly et al. 2010; Lampeitl et al. 2010; Sullivan et al. 2010; Gupta et al. 2011; Childress et al. 2013). These analyses show that, after light-curve shape corrections, SNe Ia in high-stellar-mass galaxies are found to be 0.1 mag brighter in rest-frame B than in low-stellar-mass galaxies. Recent work based on integral field spectroscopy observations of the local (1 kpc) environments of SNe Ia (Rigault et al. 2013) explains this effect as a consequence of the distribution of local star-formation conditions in nearby galaxies. They find that a population of SNe Ia in locally passive environments is 0.2 mag brighter than SNe Ia in locally star-forming environments. In higher-mass galaxies, there is an equal mix of these SNe Ia, leading to a 0.1 mag bias, while in lower-mass galaxies (M_☉ < 10^9.5) such a bright population does not appear to exist.

The NIR photometry we will obtain of the SN host galaxies will provide both reference templates for the supernova light curves as well as key observations to determine stellar mass. We will explore if these mass and environmental correlations hold in the NIR by combining our NIR supernova observations with samples from the literature together with observations of the host galaxies.

We will finally examine the late time color evolution of SNe Ia in the NIR. SNe Ia have a uniform optical color evolution starting around 30 days past maximum light (Lira 1996; Phillips et al. 1999). The full decay rate and color evolution from maximum light to 100 days will provide excellent calibration of the intrinsic color and dust extinction in SNe Ia. If SNe Ia are confirmed to be standard in their NIR late-time color evolution, then we can use a combined UV, optical, and NIR data set to make detailed measurements of the dust extinction in the SN Ia host galaxies.

We are using the WIYN 3.5 m Observatory at Kitt Peak as part of an approved NOAO Survey to image nearby SN Ia in the NIR using WHIRC. In this paper we have presented 13 light curves for SNe Ia observed in 2011B as part of this program. Within this set we have contributed 12 new standard SNe Ia to the current nearby NIR sample out to z ∼ 0.09.

We have presented an updated H-band Hubble diagram including the latest samples from the literature. Considering that we have late-time sparsely sampled light curves and a time of maximum that is accurate to a few days, it is remarkable that we measure a dispersion of our sample to be 0.164 mag when excluding 91T-like SN 2011hr. With future semesters of observing and a larger sample of SN Ia observed near maximum, we expect the dispersion to decrease as a result of more comprehensive temporal sampling. The dispersion will also improve as the optical counterparts of these SN Ia become available and the times of maximum can be more accurately determined.

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Table 5. 2MASS Calibration Stars

		WHIRC Natural System				2MASS Catalog Magnitudes
2MASS ID	SN Field	mJ	σ(mJ)	mH	σ(mH)	mJ	σ(mJ)	mH	σ(mH)	$m_{{K_s}}$	$\sigma (m_{{K_s}})$
		(mag)		(mag)		(mag)		(mag)		(mag)
2MASS 02184937−0637528	SN 2011hk	15.162	0.021	14.384	0.029	15.022	0.045	14.408	0.047	14.257	0.059
2MASS 03293834+4051347	SN 2011gy	16.640	0.025	15.883	0.040	16.565	0.102	15.827	0.122	15.450	0.123
2MASS 03573901+1009372	SN 2011ha	14.570	0.015	14.119	0.021	14.592	0.033	14.117	0.041	13.925	0.051
2MASS 07192306+5414071	PTF11qzq	16.788	0.022	16.060	0.042	16.725	0.127	15.915	0.145	...	...
2MASS 08544039+3933230	SN 2011hr	15.526	0.015	14.923	0.023	15.587	0.054	14.903	0.070	14.738	0.085
2MASS 10064485−0740334	PTF11qmo	16.325	0.022	15.570	0.038	16.376	0.109	15.583	0.099	15.429	0.221
2MASS 12200392+0925144	PTF11qpc	...	...	13.728	0.021	14.482	0.036	13.779	0.043	13.526	0.050
2MASS 12470715−0620106	PTF11qri	15.019	0.019	14.770	0.030	15.017	0.029	14.673	0.060	14.757	0.096
2MASS 21122081−0748443	SN 2011gf	15.131	0.020	14.317	0.029	15.171	0.052	14.389	0.062	14.280	0.068
2MASS 22172193+3533349	SN 2011fs	15.708	0.020	15.423	0.032	15.686	0.056	15.517	0.113	15.653	0.244
2MASS 23024227+0848225	SN 2011io	15.875	0.019	15.529	0.030	15.732	0.070	15.163	0.090	14.966	0.128
2MASS 23275179+0846392	SN 2011hb	15.745	0.024	15.021	0.037	15.684	0.067	14.978	0.099	14.838	0.097
2MASS 23505996+4643586	SN 2011iu	15.389	0.018	14.760	0.026	15.379	0.055	14.830	0.057	14.461	0.071

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Table 6. SN Ia Light Curves

Name	Date	Filter	ma	σ(m)	$\Delta _{m}^{K\hbox{-}{\rm corr}}$ b
	MJD		(mag)	(mag)	(mag)
SN 2011hr	55887.52	J	14.872	0.024	−0.042
SN 2011hr	55904.47	J	16.676	0.037	0.023
SN 2011hr	55887.52	H	15.056	0.036	−0.073
SN 2011hr	55904.46	H	15.325	0.037	−0.114
SN 2011gy	55881.50	J	17.036	0.040	−0.009
SN 2011gy	55904.32	J	18.237	0.051	−0.017
SN 2011gy	55881.47	H	15.879	0.045	−0.089
SN 2011gy	55904.30	H	16.879	0.057	−0.062
SN 2011hk	55881.36	J	17.572	0.024	...
SN 2011hk	55904.28	J	19.671	0.071	...
SN 2011hk	55881.34	H	17.027	0.033	...
SN 2011hk	55904.26	H	18.415	0.057	...
SN 2011fs	55860.31	J	17.209	0.038	−0.016
SN 2011fs	55881.17	J	17.804	0.029	−0.025
SN 2011fs	55904.12	J	19.087	0.045	−0.016
SN 2011fs	55935.11	J	19.975	0.185	0.000
SN 2011fs	55860.30	H	16.281	0.040	−0.072
SN 2011fs	55881.16	H	16.908	0.035	−0.063
SN 2011fs	55904.10	H	17.886	0.044	−0.063
SN 2011fs	55935.08	H	18.829	0.135	0.000
SN 2011gf	55860.22	J	18.200	0.044	−0.065
SN 2011gf	55881.08	J	19.004	0.046	−0.066
SN 2011gf	55860.23	H	17.126	0.045	−0.042
SN 2011gf	55881.07	H	17.917	0.052	−0.054
SN 2011gf	55904.07	H	19.081	0.188	0.000
SN 2011hb	55881.29	J	17.927	0.035	−0.083
SN 2011hb	55904.20	J	17.888	0.025	−0.072
SN 2011hb	55881.28	H	17.536	0.043	−0.032
SN 2011hb	55904.18	H	17.166	0.038	−0.034
SN 2011hb	55935.14	H	18.542	0.111	−0.048
SN 2011io	55904.16	J	19.172	0.058	−0.124
SN 2011io	55904.14	H	18.343	0.055	0.020
SN 2011iu	55904.24	J	19.096	0.033	−0.141
SN 2011iu	55935.20	J	18.899	0.114	−0.198
SN 2011iu	55904.22	H	18.612	0.038	0.047
SN 2011iu	55935.18	H	18.362	0.104	−0.060
PTF11qri	55904.54	J	19.672	0.129	−0.147
PTF11qri	55935.47	J	19.992	0.146	−0.268
PTF11qri	55904.52	H	19.402	0.301	0.027
PTF11qri	55935.45	H	19.224	0.251	−0.039
PTF11qmo	55904.50	J	19.963	0.075	−0.175
PTF11qmo	55935.42	J	19.966	0.163	−0.275
PTF11qmo	55904.49	H	19.176	0.068	0.083
PTF11qmo	55935.39	H	18.729	0.099	−0.058
PTF11qzq	55904.36	J	19.056	0.043	−0.136
PTF11qzq	55904.34	H	18.635	0.078	−0.065
PTF11qpc	55904.56	H	19.795	0.108	−0.079
PTF11qpc	55935.50	H	20.122	0.225	0.126
SN 2011ha	55881.40	J	20.434	0.130	−0.756
SN 2011ha	55881.38	H	20.627	0.191	0.018

Notes. ^aMagnitudes reported in the WHIRC natural system, which is referenced to 2MASS at $(m_J^{\rm 2MASS}-m_H^{\rm 2MASS})=0.5$ mag. ^bK-correction as calculated by SNooPY (Burns et al. 2011). Subtract K-correction value (Column 6) from reported natural-system magnitude (Column 4) to yield K-corrected magnitude in the CSP system (Stritzinger et al. 2011).

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The observations presented in this paper came from NOAO time on WIYN under proposal ID 2011B-0482. A.W. and M.W.V. were supported in part by NSF AST-1028162. A.W. additionally acknowledges support from PITT PACC and the Zaccheus Daniel Foundation. Supernova research at Rutgers University is supported in part by NSF CAREER award AST-0847157 to S.W.J. The "Latest Supernovae" Web site²⁶ maintained by David Bishop was helpful in planning and executing these observations. We thank the referee for helpful comments and the careful reading of our work. We thank Chris Burns for his significant assistance in using SNooPy. We thank Sandhya Rao for her assistance with IRAF. We thank the staff of KPNO and the WIYN telescope and engineering staff for their efforts that enabled these observations. We thank the Tohono O'odham Nation for leasing their mountain to allow for astronomical research. We thank the Aspen Center for Physics for hosting the 2010 summer workshop on "Taking Supernova Cosmology into the Next Decade" where the original discussions that led to the SweetSpot survey took place.

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

Facility: WIYN - Wisconsin-Indiana-Yale-NOAO Telescope